In the latest high-profile hacking incident involving social media service Twitter, an official AP account reported that explosions at the White House injured US President Barack Obama. Shortly afterward AP spokesman Paul Colford told Reuters the tweet was "bogus."

White House spokesman Jay Carney told reporters that Obama was fine soon after the tweet went out a little after 5pm Irish time.

A group calling itself the Syrian Electronic Army, which is supportive of that country's leader, Bashar Al-Assad, later claimed responsibility on its own Twitter feed for the AP hack.

The group has also claimed it was behind past hacks of Twitter accounts for National Public Radio, BBC and CBS's "60 Minutes" program, among others.

The message, which went out to the AP's nearly two million Twitter followers, sent the S&P 500 and Dow Jones Industrial Average plunging sharply before they recovered. Stock and bond futures also were affected.

Some traders blamed automatic electronic trading for the sharp fall and recovery. A spokesman for the Securities and Exchange Commission declined to comment.

The AP's Twitter account was suspended shortly after the fake tweet, and the news organisation later reported that the tweet came after hackers made repeated attempts to steal the passwords of AP journalists.

A Twitter spokesman declined to comment on the AP breach, saying the company does not comment "on individual accounts for privacy and security reasons." An FBI representative had no immediate comment on the AP hacking incident.

In what one trader described as "pure chaos," the three-minute plunge triggered by the tweet briefly wiped out $136.5 billion - approximately €105bn - of the S&P 500 index's value, according to Reuters data.

Earlier this year, Bloomberg's professional trading platform started incorporating tweets. On Tuesday, spokeswoman Sabrina Briefel said the fake tweet did appear on the Bloomberg terminal. She said the company was not reconsidering its decision to include tweets